This invention relates to a hose for fuel piping purposes and more particularly to multi-layered or laminated hose for fuel piping used for, for example, automotive purposes.
Evaporation and/or transpiration of fuels from various types of fuel tanks raises serious problems of environmental pollution and destruction of environment. Thus, there is a social tendency to impose legal controls on such evaporation and transpiration of fuels and, actually, in the United States there is a regulation which imposes a legal control on cars and automobiles to regulate the transpiration to a maximum level of 2 g/24 hrs or less. Moreover, it is now suggested to amend this regulation to be four times severer at one effort than ever for the cars as from the 2004 year model.
A conventional fuel hose has a multi-layered structure having an inner layer made of synthetic resin material which has a low fuel permeability. However, in order to meet the severe requirement of restriction in transpiration, developments, new contrives and modifications have been demanded strongly with respect to materials and structure thereof.
Recently, it has been preached to collect various kinds of material for recycling purposes. The hose for fuel piping which requires flexibility, weatherability (that is, atmospheric corrosion resistance or weather proof and flame resistance generally has an outer layer of rubber. However, it is extremely difficult to successfully proceed recycling of rubber and this requires a high cost. In addition, since the conventional hose has a structure that an inner layer of synthetic resins and an outer layer of rubber are firmly adhered or welded to each other, such a structure makes it quite difficult to proceed recycling of resins although the resin is inherently recycled relatively easily.
In order to meet with the requirements for prevention of fuel transpiration, many attempts have been made as disclosed in Japanese Patent Publications (Unexamined) No. 6-221481 and No. 7-205327 and these attempts are largely classified into three types of structure, as described below.
(a) a multi-layered rubber hose made of FKM (fluoro-rubber, fluorocarbon rubber);
(b) a nylon type resin hose with an outer circumferential coverage of rubber hose, which is made by inserting a resin hose element into a separately is formed rubber hose element; and
(c) a rubber hose with an inner circumferential lining of nylon type resin adhered to an inner surface of the rubber hose, which is produced by spraying resin powder to an inner surface of the vulcanized rubber hose.
The multi-layered rubber hose of type (a) is inherently made of a rubber and therefore it is less permeability-resistant. Thus, in order to meet and satisfy the new and severer regulation described above, a substantial increase in thickness of the hose is required, which results in substantial increase of production cost and increase of weight, and consequently brings about some difficulties in recycling.
With respect to the resin hose of type (b), it has a basic problem that the nylon type resin is not adaptable to alcohol, and when nylon type resin is molded by blowing, drawdown appears violently to result in difficulty in control of thickness. In this structure, although the inner and outer layers are not adhered to each other and only the inner layer of nylon type resin can be recycled, the outer layer of rubber is not easily recycled.
The hose of type (c) is similar with the type (b) in a sense that nylon type resin is used. However, the nylon type resin of type (c) hose is firmly adhered to the rubber hose and therefore it is very difficult to proceed recycling as well as rubber itself.
It is, therefore, an object of the present invention to provide a new laminated hose which meets the requirement of the forthcoming new regulation of transpiration and permits easy recycling and reduction of weight as well as production cost.
According to the present invention, there is provided a hose for fuel piping comprising:
an inner layer portion having a single layer of a thermoplastic resin of a low fuel permeability, the inner layer portion having a thickness of at least 0.3 mm at a maximum thickness portion thereof, and
an outer layer portion of a thermoplastic elastomer,
wherein the inner layer portion is laminated to the outer layer portion by a bond strength of 0.6 kgf/cm or less.
In a modification of the structure described above, the inner layer portion of a thermoplastic resin having a low fuel permeability can be coated with a thermoplastic resin to thereby form into a multi-layer structure.
In the hose of the present invention, since the inner layer portion has a single layer of a thermoplastic resin having a low fuel permeability or otherwise the thus formed single layer is coated with a thermoplastic resin to form a multi-layer structure of the inner layer portion, the inner layer of either configuration has a low fuel permeability material and, therefore, the hose of the invention can meet with the requirements of the new, severer regulation. Further, in either case of the inner layer portion, a single layered and multi-layered configurations, the maximum thickness portion of the inner layer portion is set as thick as 0.3 mm or more, the structure is satisfactory for both strength and rigidity for the purpose of maintaining the shape of the hose. On the other hand, the outer layer portion which is made of a thermoplastic, rubber-like elastomer can satisfactorily meet the requirements such as flexibility, shock-resistance, weatherability, etc.
Further, the inner layer portion and the outer layer portion are laminated with each other by a bond strength of 0.6 kgf/cm or less at a normal condition and, therefore, each of the inner layer portion and the outer layer portion can be peeled off or removed from each other and consequently both the inner and outer layer portions can be recycled. The term xe2x80x9cbond strengthxe2x80x9d used herein intends to mean a peel strength specified by JIS (Japan Industrial Standards) K6330-6. This value of the bond strength, which is 0.6 kgf/cm or less as defined in the present invention, is a bond strength which can be obtained without any specially positive bonding treatments and which is a natural bonding strength generated and obtained at the time of a simultaneous molding of the both inner layer portion and the outer layer portion. Thus, the value of the bond strength described above is such a strength that removal can be effected easily by manual peeling operation.